1. Field of the Invention:
This invention relates to acoustic imaging systems for obtaining an acoustic picture of an underwater target area of interest.
2. Description of the Prior Art:
A variety of underwater acoustic cameras exist utilizing the principles of sidelooking sonar to image a target area laterally of the camera apparatus.
A transmitted pulse of acoustic energy is utilized to sonify the target area, the returns from which are received by multiple receiver beams as the pulse propagates from a minimum range out to a maximum range of interest. A display device then portrays these returns so as to display the area under investigation and any targets on it. The multiple beams may be formed electronically such as, for example, described in U.S. Pat. No. 3,742,436 or may be formed utilizing a plurality of individual transducers in conjunction with a lens system as in U.S. Pat. No. 3,898,608.
For various military missions, it would be desired to image a relatively wide area, for example 360.degree. below the apparatus. U.S. Pat. No. 3,742,436 includes such a system utilizing a single rotating beam, however this method is too slow to be practical where the apparatus is to be towed at a moderate rate of speed.
Some imaging systems utilize a spherical acoustic lens in conjunction with a plurality of transducer elements, however such lens is not well suited because it produces focusing in elevation as well as azimuth. For high resolution work, a vertical beam angle of 30.degree. to 60.degree. and focusing in azimuth only, is desirable.